Not Applicable
1. Field of the Invention
This invention relates to cardio myopathy and its effect on electrical activity of the heart. More particularly, the invention concerns a pacemaker and related instrumentation for restoring heart rhythtn functionality to a heart.
2. Description of the Prior Art
By way of background, the human heart is a large muscle consisting of a series of pumping chambers that are carefully controlled by a specialized electrical system designed to deliver timed contraction signals to the muscle cells associated with each chamber. This electrical system attempts to regulate the heart rate between a range of about 60-100 beats per minute. At the beginning of a heart beat, an electrical signal originates near the top of the right atrium. A network of specialized nerve cells, known as the xe2x80x9csino-atrialxe2x80x9d or SA node, generates the electrical signal. Conduction pathways carry the electrical signal to the muscle cells of the left and right atria, causing them to contract and pump blood into the ventricles. Additional conduction pathways carry the electrical signal in a downward fashion to additional nerve tissue known as the xe2x80x9catrio-ventricularxe2x80x9d or AV node. Here the electrical signal is slowed slightly as the ventricles fill with blood. The AV node electrically separates the upper and lower chambers of the heart and acts as a gateway to an additional bundle of conductor cells known as the xe2x80x9cbundle of His.xe2x80x9d The bundle of His divides into right and left branches in the lower chambers of the heart to carry the electrical signal to two final groups of nerve tissue, known as the Purkinje fibers. The Purkinje fibers on the left and rights side of the heart respectively deliver the electrical signal to the muscle cells of the left and right ventricles. Because of the specialized way in which the electrical signal is transmitted, the ventricles contract almost simultaneously.
With normal electrical conduction, the cardiac contractions are very organized and timed so that the atria contract before the ventricles, and the heart rate is maintained between about 60 and 100 beats per minute. This provides the major pumping action of the heart, allowing blood supply to reach the tissues of the body.
Sick sinus syndrome is a condition in which the SA node is impaired, such that a heart rhythm disturbance results. In particular, the SA node loses the ability to initiate a heartbeat or increase the heart rate, and the heart may not be able to respond effectively to the body""s changing circulation demands. Heart block is a condition in which the tissue constituting the AV node is impaired and the electrical impulse from the upper portion to the lower portion of the heart is slowed, blocked or made irregular, such that ventricular contraction is slowed. A common cause of sick sinus syndrome and heart block is nerve cell damage caused by a heart attack or other cardio myopathic condition. Other causes may also produce these conditions. The treatment is usually the implantation of a mechanical pacemaker in the patient""s upper right shoulder, with one or more shielded leads being attached to the heart to generate electrical signals that pace the heart at a suitable rate.
Although many advances have been made in the implantable pacemaker art, a number of disadvantages still exist. Pacemaker implantation, for example, is generally expensive and typically requires hospitalization, operating-room time, and post-operative observation. The treatment is also associated with some risk. A pacemaker, moreover, although capable of increasing its electrical output under changing conditions, such as exercise, cannot alter its signal generation rate as efficiently as the heart""s own electrical system. It is also necessary to replace a pacemaker every 5-7 years insofar as such devices run on batteries.
It would be desirable if the foregoing disadvantages of existing implantable pacemakers could be overcome. What would be particularly useful is a pacemaker that is (1) readily implantable, preferably without surgery, (2) operates virtually indefinitely without replacement, and (3) provides normal or near normal heart rhythm functionality, including the ability to produce rapid changes in heart rate when necessary.
U.S. Pat. No. 5,103,821 (the ""821) discloses a method of providing biological pacemaker as an alternative to mechanical pacemakers. In accordance with the disclosed method, SA node cells are removed from the heart and cultured to generate a critical mass of SA node cells of sufficient quantity to generate a depolarization wave capable of stimulating the cells of the myocardium to ensure normal or near normal pumping action in the heart. The critical mass of SA node cells are then implanted in the myocardial tissue of the right ventricle, preferably near the ventricular apex, to provide biological pacing for the heart which is sensitive to and variable with normal increase and decrease of output demands on the heart. A new SA node is essentially created and it is said that the heart""s natural SA node may need to be destroyed in some cases to prevent xe2x80x9ccross-talkxe2x80x9d between the newly implanted SA node cells and those remaining in the right atrium.
A deficiency of the method disclosed in the ""821 patent is that it involves the recreation of an SA node at a new location in the heart. This may affect the heart""s pumping action insofar as SA node activity is now occurring in the right ventricle rather than the right atrium. Moreover, the above-mentioned cross-talk may occur unless the original SA node is completely removed. A further deficiency of the method of the ""821 patent is that it requires the use of three different catheters to perform the procedure. A locating catheter is required to locate the existing SA node so that SA node cells can be removed for culturing. A removal catheter is used to remove the SA node cells. An implant catheter is used to implant the cultured SA node cells in the right ventricle.
Applicants submit that improvements in biological pacemaker technology are needed. In particular, it would be desirable if dysfunctional SA node tissue (or AV node tissue) could be treated in situ and restored to normal or near normal activity rather recreating node functionality at an entirely new location, and possibly destroying the original node. A multi-purpose catheter that can be used for both node mapping and cell implantation, or for node mapping and cell removal, or perhaps for all three functions of mapping, removal and implantation, would also be desirable.
The foregoing problems are solved and an advance in the art is obtained by a biological pacemaker and implantation catheter for restoring normal or near normal heartbeat function without a mechanical pacemaker. The biological pacemaker is provided by a bridge of implantation cells, such as cultured autologous SA or AV node cells, nerve cells, stem cells, or ganglion cells, that are introduced into an area of electrical malfunction, such as an impaired SA node or a blocked AV node. The implantation cells grow to form a conductive cell bridge around the malfunction area so that a new pathway is provided for the electrical signals responsible for triggering ventricular contractions. The impaired node is thus repaired and not rebuilt at a new location as in the ""821 patent described by way of background above.
The implantation cells can be introduced into the malfunction area in any suitable fashion, but are preferably injected via an improved catheter that can be used for both node mapping and cell implantation. The catheter has a central nerve cell injection needle connected to a syringe via a cell injection tube, and two elongated lateral stabilizing needles. The catheter further includes instrumentation for locating a blocked SA or AV node by way of electrical, ultrasound and/or visual probing. Further instrumentation can be added for cell removal.
The catheter is inserted into a blood vessel in a patient""s leg, arm, shoulder or the like, and advanced until the catheter""s distal end is located adjacent to the malfunction area. The catheter is constructed so that its distal end can be bent so that the three needles are facing the malfunction area, which is located using the catheter""s locating equipment. The two stabilizing needles are advanced into the heart wall to stabilize the catheter and the nerve cell injection needle is advanced to inject the implantation cells. The nerve cells are injected via the syringe.
The catheter can be bent using a pull cable that is attached to the catheter""s distal end, and which may run inside a cable sheath back to the catheter""s proximal end. The two lateral stabilizing needles are flexible needles that may be connected together as a unit by way of one or more needle guides. The guides preferably have a central aperture for receiving the cell injection tube that runs from the syringe to the cell injection needle. An injection tube sheath can be mounted to extend between the apertures for slidably receiving the cell injection tube. The catheter can be made from plastic tube material but most preferably has two walls defining a main hydraulic sheath that can be filled with saline or water. The main hydraulic sheath is filled to stiffen the catheter during insertion. At least the distal end thereof can then be emptied to allow the distal end to be bent. During insertion of the catheter into a patient, all of the needles are retracted. When the distal end of the catheter has been positioned adjacent the block site, the tip of the catheter is bent and the lateral stabilizing needles are extended to pierce the heart wall. To facilitate bending, the pressure in the main hydraulic sheath can be relieved. The stabilizing needles stabilize the catheter against the movement of the beating heart. The cell injection tube and needle are then extended to inject the nerve cells. Preferably, a small bladder at the distal end of the hydraulic sheath remains pressurized with fluid to form a seal against leakage during nerve cell implantation.